Infection on Titan
by thelarker
Summary: Manhattan's monster, Alex Mercer codenamed 'Zeus' is in the process of saving Manhattan from nuclear destruction. At the same time, in a different place atop the Wall of Rose the trainees are getting excited at the prospect of their future, unawares of the threat that is rapidly approaching...
1. Prologue

Humanity biggest threat, Manhattan's monster, grit its teeth as its hand pressed on its right knee to force itself to stand and watch the horrid pink mountain of muscle that had almost killed it so many times in its last fight. With a meaty thud, it crumpled to the ground.

The steel-grey eyes it mimicked remained on its greatest foe for one more second, as it lay dead in front of him, then it turned around and headed for one of the very few aircraft that had been left intact in the fight that had severely damaged the ship: it went over to the atomic bomb left on the pallet, with its timer ticking down. The virus knew that it had only a few minutes left and hurried to fasten the clamps and buckles around the bomb so it would not fall off the pallet, linking the explosive device to the combat helicopter that it would get into next.

Remembering all the experience of the dozens of pilots it had consumed, it flicked a few levers, pushed the correct buttons and started spinning the blades of the aircraft that would save Manhattan from certain doom. Taking to the air, Zeus pointed the chopper toward the outer sea, away from the mainland: it knew it had only moments to win this race. With the countdown ringing in its mind, the shapeshifter finally swung by the destination the scientists inside him told him was going to save the people in its city.

With the last push of a button, it released the link holding the bomb afloat below it, dropping it into the mass of water below: without skipping a beat, it turned the helicopter back from whence it came and tipped its nose slightly down in order to fly back at top speed. Its aim was, of course, to outfly the range of the device that would have leveled the metropolis... but it knew that it could not outrun it completely, that the blast would catch up with it in just a few seconds.

Blinding light, followed by a deafening explosion and smoldering heat reached him from behind, the shockwave flipping over the helicopter, which nonetheless was hurtling toward the quarantined area. The seat it sat on was boiling hot, as was the metal and plastic pressing forward now, barely solid. Nevermind the glass, which had cracked and shattered immediately, as the biomass enveloped itself in the hardest shell it could, one that could withstand point-blank shots from tanks and shrug it off with very little damage.

As the armored Zeus hurled through the sky, something about its seat felt... off, but it kept its eyes shut until the heat was bearable again: then it felt as though it was not inside of a helicopter anymore: the wind and rock crashing on rock noises tipped if off in that regard and it opened its eyes to look around. The scenery that it saw was amazing and unfamiliar: a blue sky, with little clouds all around on top of grassy plains and small buildings.

 _Something's not right_...

The voices of many screamed at the same time, as it saw a human towering over a small house: no, that was not a human, it was something different. It was naked and a second look revealed that its proportions were glaringly off: its eyes were bigger than a normal human and it certainly had features that could only belong to something monstrous. It lacked genitals too, for that matter. As the virus pondered this, it looked back, toward where it had felt the seat before and it realized that there was no helicopter anymore.

In its stead, it saw what could only be described as a gigantic- no, titanic wall, and a huge cloud in front of it. _Is that a human_? The virus pondered, as it saw the silhouette of someone moving toward the wall, in a swinging motion. As it exited the curtain of fog, Zeus was certain that it was a young man, probably not yet an adult who was landing on the side of the wall with the help of a rope, attached to somewhere on the wall probably.

Regardless of the situation, the monster of Manhattan focused on something more pressing: it extended its legs in order to use the direction of the wind and turn downside up just as the thick, bulletproof shell it wore returned into the rest of its biomass. Now that it was not falling head first into the ground anymore, the tendrils that made up its clothes shot out as a webbing between its limbs, a measure it could take in order to quickly stop its current direction mid-air and choose a new direction to glide towards!

After inhaling a bit- the monster then exhaled with such force that it expelled the air contained within him and dashed forward, toward the big gray wall. Its eyes were focused only on that and then finally noticed the debris that had been raining down: Zeus' face slammed against a broken rail track and after that, he crashed back first into the earthy ground. _I hate this place_. Was the first thought that came to mind now, as it heard giant footsteps advance toward its current position.

The blacklight virus wrested the piece of metal out of its face which was already rearranging into that of Alex Mercer when it noticed that the naked giant was already at arm's length... at least for the titan. Speaking of which, with wide eyes, it reached down to grab at the tinier monster: with a thought, the tendrils that formed its right arm rearranged into the form of a menacing blade, at least half as big as the average human. With a lightning-fast strike, it cleaved into the wrist of the outstretched hand and cut it right off the limb, the big appendage landing on the ground in front of it with a loud, meaty thump.

"What're you trying to-" The shapeshifter was about to say, when the whole giant jumped forward, face first to try and eat it. It could tell, because the titan's mouth was wide open, flashing some very sharp teeth: shocked speechless from such a display, Zeus did not react in time and soon it felt the pain of losing half of its leg's biomass, swallowed whole by this creature. Its tendrils were already busy reforming its feet and lower shins when Zeus furrowed its brows and gnashed its teeth in anger.

"WHAT THE FUCK IS YOUR PROBLEM ASSHOLE?!" The irate virus yelled at the monster as its blade scraped the cheek and caught part of the jaw, making the whole swallowing thing a lot more difficult for the giant. "I'M GOING TO MURDER YOU!" It prophesied and turned the blade on its right and the left, humanoid hand into big paws, with claws made of sturdy metal. With such lethal weaponry equipped, Zeus started to rip into the flesh with glee: it gave way very quickly, the only thing offering more resistance being the spine.

... _what's this- resistance_?

It could feel new resistance with each strike, as if the giant was regenerating its wounds, similarly to how blacklight had formed new feet in a matter of seconds: it was not as fast, though, Zeus gathered as the light of day once more shone on the gore-splattered face of Mercer. Digging its claws in, it widened the slash it made and crawled out of the hole in the back of the neck it had made, just like a rat tunneling through a human's flesh to regain its freedom.

Jumping down from the spasming giant, Blacklight wondered how it could still move after that: it was clearly standing up and the wound it had on its hand was smoking, pink flesh already growing into what the virus could only assume would be another hand. Immortal enemies? It clicked its tongue in annoyance and frowned, before stepping back a bit, in order to get out of arm's reach for the creature.

Looking back at the wall, the cogs in the shapeshifter's mind turned. _First, I must understand this world. This giant will probably attack me again, so I should go while it is still regenerating... I should consume a local_. Once it had determined its new priority, Zeus turned its back on the monster and sprinted toward the wall, intent on proceeding with his plan.


	2. Chapter 01: First contact

I do not claim to own Prototype's Alex Mercer or Attack on Titan's setting and characters. All of them are of their own respective authors/owners. Please support the official release!

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Blacklight ran over the grassy field, avoiding the beaten path in favor of a shorter distance to the gigantic wall. Looking up, the virus did not see the human dangling from the top at the end of a rope from before but that hardly mattered right now: the construction was only a few steps away after all. As it did back in Manhattan, it did not stop as it ran full speed ahead toward the wall, tendrils shooting out of its extended leg to pierce the wall ever so slightly to allow it to speedily make its way upward.

It had not taken long and Zeus landed on the wall after a short jump: as its gaze shifted downward, it saw the pandemonium unleashed... it looked like a river had burst its banks, only with people. The inhabitants of this place were running for dear life, and the weakest were trampled by their panicked peers, all running away from the closed gate that had been destroyed. This phenomenon was not unfamiliar to the 'Terrorist' watching it all with cold, steel eyes, examining the first few giants lumbering in, as they were intercepted by regular-sized people, flitting about to and fro thanks to a device strapped to their waist.

This was as much as it could make out from this distance before its attention was caught by a loud "HEY YOU! Who the hell are you?" The shapeshifter turned to the owner of the panicked voice, glowering at the stranger who had addressed it in a tone that was clearly not friendly. "STOP! No sudden moves or I will shoot!" The man held what appeared to be an old firearm, that would have belonged in the 16th or 17th century the virus surmised. It lifted its right hand and took a first step toward the stranger, opening its mouth to speak.

"Can you understand what I say?" Was what it said in a gravelly voice as it inched closer. "I SAID STOP, ARE YOU DEAF?! AND SPEAK JAPANESE, STRANGER!" The panicking soldier repeated, raising his voice as if that would help any. Zeus simply took another step, his cold glare like icy daggers aiming to strike the man's hazel ones. The rifleman gave no sign of lowering his weapon, instead, he only gripped it tighter.

"DON'T COME CLOSER: I WILL SHOOT" He warned a second time: there would be no third time, that was certain. However, Blacklight had no intention of backing down and got closer and closer once more before the soldier narrowed his eyes and pressed his finger on the trigger, squeezing it tightly. With a loud - **BANG** -, he shot the lead projectile at the unknown threat: that did not stop the virus from advancing, neither did it slow down. On the contrary: it only looked angrier. The man had closed his eyes briefly and his expression went very pale when he reopened them... clearly he was incredibly frightened when he saw how this foreigner appeared completely unharmed, despite being shot at what was basically point-blank range. "You shot me... and you aimed for my heart: you really wanted to kill me." It said, in a tone that conveyed ice-cold rage and suddenly claws replaced its hands. "It's only fair I try to kill you, too." Even if the soldier did not understand English, the message seemed to have reached him: his scream of alarm " **M-MONST** -" was cut short when said monster thrust its blades into his neck, tendrils shooting out from its limb and piercing the body.

A short moment later, Zeus placed a human hand on its face, the memories flooding its mind. _So they are called Titans_... It discarded the vertical maneuvering equipment, tossing it on the outer side of the wall: the virus had already determined it could not use it, due to the nature of its biomass that made it several times heavier than a normal human. It had a lot to think about... the weakness of the giants, this new world that knew nothing of America or Manhattan, where it was from. After a minute, it decided to test out the knowledge it had gained on the titan that had tried to kill it: pacing toward the outer side of the wall, it spotted the 14 meter tall titan that had tried eating the virus before walking a pretty good distance toward the entrance, clearly with the intent to reach the town and the populace living in the town.

With a leisurely pace the shapeshifter jogged toward the edge of the wall and leapt in the direction of its quarry: once it had made sure that it was en route to collide with the titan, its arms bulged with black tendrils, the biomass hardening its limbs to the extremes and making both limbs a mockery of their human counterparts. With primed hammerfists, Manhattan's monster dropped like a meteor on top of the hapless giant, reducing it into a pink stain on the ground with an earth-shaking - **BOOOOOM** -...

 _That was disappointingly easy_.

With its enemy obliterated, to the point its constituent cells were splashed across the field, the virus turned its hammerfists into hands once again, now thinking back to the memories of the local soldier. _Mhm... In the first attack, an armored titan appeared: maybe it will be here today, too_. This was worth checking out: with another brief sprint, it ran on top of the wall for the second time today in order to gain its vantage point once again. The chaos below had not died down yet, people were still panicking, although most of them had been able to reach the other side of the city.

Unfortunately for it, the armored titan was nowhere to be seen yet: with a frown, it changed into the appearance of the soldier he had just consumed and jumped down into the citadel. It extended its arms and glided the last few meters in order to avoid leaving a crater like the one it left after landing on its guinea-titan. It looked like the titans were making short work of the vanguard around here, so the virus elected to run in the alleys and secondary streets toward the inner gate in order to avoid undue attention. Jogging along at around fifty kilometers an hour, Blacklight looked at the chaos unfolding around it, avoiding detection from the soldiers using their maneuver on top of the rooftops.

As it sprinted into a street, it heard a loud crash, like a body hitting roof tiles and blood spraying down on the streets: at the same time the bioweapon stopped its running when it saw a titan landing after having jumped. That titan reminded it a bit of a Cheshire cat, only with slightly less pointy teeth: some of them had a fresh blood coating. It also saw another titan, with an expression that could be described as a mix of disappointment, annoyance and anger: those big eyes seemed to be peering and judging Zeus among other people. That's when a cry of desperation roused the virus of its thoughts: about three people charged at the jumping titan with the fresh blood and all three screwed up really badly. One of them, a girl with her shoulder-length black hair tied into two loose pigtails, was slammed into the wall just a couple of steps away from the walking, talking bioweapon.

The former terrorist, in the guise of the soldier it had consumed, moved faster than the titan and grabbed the young woman's arm, speaking up as it helped the girl to stand "Now isn't the time to take a nap, you could end up as dessert for these uggos!" And, as if the shapeshifter had been heard, the peering titan attempted to grab them both: but the virus was ready for that and had already started jogging toward the gate that led to the inner city, avoiding any other titans on the way with the injured soldier woman secured over its shoulders. "Thank you.." The girl mumbled to the shapeshifter, who replied dispassionately "No problem."

At the gate, Blacklight saw the smoldering corpse of a titan in the middle of the street and a voice addressed it from the rooftops. It was a black-haired girl with a red scarf who had just discarded a couple of blades from her maneuvering gear. "What happened to Mina? Where's the rest of the squad?" The virus shrugged and answered, since Mina looked like she was still out of it after everything that had happened. "The others were back there" and it pointed back to the way it came, before commenting "-with a couple of titans." This was all the explanation the girl needed apparently, as she turned that way and took off: on his end, the virus dropped the soldier into the arms of a couple of officers that would handle the wounded and the injured, before turning back.

The men that took charge of Mina were about to turn to the soldier who had brought the trainee back, but he was already running into the town center, where the titans were most likely to pop up. Blacklight's mind worked tirelessly as it was running in the alleyways like a common thief, avoiding any and all bigger streets that could get it spotted by one of the soldiers: it took him quite a bit of time to return to the place it was before, but thanks to its very good sense of direction it returned without getting stopped by the military or titans.

It stopped when a pile of debris blocked its way: that's when it heard voices from the roofs and looked up with its heat vision and what it found were a couple of dozen humans standing on the roofs surrounding it. It settled in the alleyway, hiding away from them in order to avoid being spotted: they would become suspicious of its current persona, since it did not wear the ODM gear. So for now, it stayed quiet in order to listen to what was being said.

"-sorry for letting my personal matters interfere, but have you seen Eren's team at all?" came the familiar voice of the scarf-wearing girl it had seen before.

Unfamiliar voices of a woman and a man replied that she did not, however there was Armin who was with Eren's team a little bit over there. He could hear her hurried steps as she moved to greet who Zeus could only guess was Armin.

"Armin, are you injured? Is everything okay?" ... "-where's Eren?" The silence after that could only mean one thing. The boy replied, sobbing "In the trainees squad #34... our team... Tomas Wagner, Nack Teaz, Millius Zermunsky and Eren Jaeger... the aforementioned four were killed fulfilling their duty..." The silence before had been nothing compared to this one, even if it lasted less when a girl muttered incredulously.

Said team 34 had been mostly obliterated and Blacklight crossed its arms, trying to make out the rest of the boy's muttering now: it could not but the girl spoke up again in an ice-cold rage, hidden under an emotionless mask. "Armin, calm down. This is neither the time nor the place to be emotional. Stand." She stepped away and to the edge of the roof. "Marco, if we eliminate the titans swarming the HQ, everyone can replenish their gas reserves and climb back up the wall. Is that correct?" The young man named Marco confirmed it and voiced his concerns about them being able to, even with the help of Mikasa.

But she was undeterred "We can do this." She said, without a shred of a doubt "I am strong... extraordinarily so... much more than you guys!" The monster of Manhattan raised a dark brow, hearing that. "...Therefore I am perfectly capable of kicking those titans scumbags' collective ass... including on my own, if I have to." And then, in a challenging, yet emotionless tone that disguised her inner turmoil "Are you all such a bunch of incompetents? You gutless, spineless cowards! For shame... for shame indeed. You just stay there and watch in helpless envy... Yeah, you do that."

Voices of dissent let themselves be heard, doubting her words, challenging her and telling her it was impossible, but Mikasa -that was her name- replied "If it is, then I'll die: it's that simple. But if I win, I get to live. You don't stand a chance to win... unless you fight..." and with these words, the strong girl sprinted off, the other soldiers gasping and gawking in awe and skepticism. Zeus could tell that Mikasa's words had hit the bullseye as the whole group of soldiers was left behind in stunned silence.

"I DON'T BELIEVE LEAVING A COMRADE TO FIGHT ALL ON HER OWN WAS EVER PART OF OUR FORMATION?! COME ON GUYS! OR WE'RE GONNA TURN OUT TO BE SPINELESS COWARDS, ALRIGHT!" The leader yelled out and the war cry of the humans roared to heaven, making the Monster smile.

 _These guys are amusing... let's see how it goes_.

And with that thought, the monster decided to follow the footsteps of the soldiers, who rushed in pursuit of Mikasa: staying on street level, it aptly dodged any and all titans trying to grab it by ducking, tumbling and jumping through their legs and outstretched arms. The nimble virus used the soldier's distraction to avoid detection from both titans and humans: it was quite fast, keeping pace with the ODM gear quite well. After a bit, though, it opted to loop around to the right side of the onrushing soldiers, sprinting faster so as to catch up to the leader, Armin and Mikasa.

No sooner had it done that, then Armin yelled out in alarm "MIKASA!": Blacklight quickly changed alleyways and used thermal vision to find the smallest points of heat that would be the humans it was pursuing. It found one close to the ground that was being approached by a bigger entity of heat- a titan no doubt. Quickly, Zeus made its way over there, switching back to normal vision: a titan was approaching the kneeling form of Mikasa. Switching back to its main form, it watched as the girl stared at the ground first, to the sky second and finally to her weapon's broken blade. From behind the big titan, Mercer couldn't suppress a slight smile when she got up, her willpower pouring from her eyes as she looked straight at the titan and yelled at the top of her lungs. A fine battle cry.

 _That settles it, you're going down big guy_. Blacklight decided, changing its left hand to a clawed whip, which was thrown at the towering titan that was nearing Mikasa fairly quickly. The claws dug into the back of the huge humanoid and Mercer dug its tendrils into the ground, rooting itself and the titan in place, as armor started to form all over its black jacket and blue faux-jeans. Now wearing its black exoskeleton of biomass, it looked up in surprise when it saw the enormous humanoid flying to the ground with its head twisted to an unhealthy degree.

In the blink of an eye, it understood: another titan was standing where the downed one had just a moment before, its right hand balled into a smoking fist as it opened it's huge jaw and gave a monstrous, rage-filled roar before rushing forward to curb stomp the downed titan one, two, three times... Alex ducked and jumped away, toward the inner part of the street: he saw Mikasa there, staring boggle-eyed at the titan killing its own kin. She was so surprised, she barely registered a shadow jumping away from the wall and to her side: the virus grabbed her waist and slung her over its shoulder, jumping to the rooftop.

As it landed on the rooftop it set down the girl on the roof tiles: she regained her senses after the landing and pointed her broken knife at the monster immediately in alarm. "Who are you? Are you an enemy?" As she asked this, two boys zipped on over, encircling Blacklight. "MIKASA! ARE YOU ALRIGHT?" Came the question of the blonde to the left of the virus. "What is this?" The second one, with very short hair, asked and kept his blades at the ready.

"I am Alex Mercer. You can call me Alex though." The Blacklight virus introduced itself, retracting the exoskeleton slowly in order to reveal its face to the three humans. It had been a while since it had discovered that it was not Alex Mercer anymore... but it was the persona that was most commonly used back in Manhattan.

So it... no... He revealed his face to Mikasa, Armin and Conny who were looking at one another, bewildered. "While I would love to stand around and chat, you guys are running out of time and gas, are you not?" He recalled what had transpired before and then suggested "I am not your enemy. If I was, I'd have left you down there with the titans... speaking of..." he turned around while the three humans looked at each other, mulling over the things that Zeus had just said.

When they turned to look at what Alex was watching, they saw the 15-meter class titan from before stepping up to another of the same height. They were shocked speechless when the giants roared at one another and the athletic one, with defined muscles all over, took a fighting stance and waited for the other one to come at it. When the other titan stepped up to the challenge and charged, the abnormal one charged a powerful swing that slapped the head of the titan clean off, sending it flying with the grace of a brick into a house closeby.

"DUCK!" Mercer yelled immediately, crouching down and dodging the gigantic airborne appendage, the other three all copying him.

That was not enough for the abnormal, though, as it stomped on the nape of the neck that was exposed with one powerful kick, killing its kin. Armin voiced his incredulity "It went... for a lethal strike?! Is it just me or did it do it on purpose?!" Conny voiced his suggestion to move before it would attack them. "Doesn't look like it's interested in humans." Alex noted, finishing his comment "Otherwise it would have attacked us a while ago." Mikasa interjected after this, saying "It even took a fighting stance... just what is going on? And what are you?"

She had a point, the other two boys seemed to say with their looks, as they glanced over to the virus once more. The latter turned to look at them again, saying "We don't have much time so I'll keep it short. I was a human, not too long ago, researching weapons: I was exposed to my research and now I have become a weapon. I will destroy the titans here, but you still have to be careful on your way to HQ." In his short lifespan, the virus had learned that mixing truth with one's story made it more believable: thanks to this it was able to keep the three from asking more questions. At least for the time being.

Armin looked at Alex with a piercing gaze: behind his expressionless facade, the virus thought. _I will have to be careful with this guy_... Before he was roused from his intentions when Conny repeated that they had to be on their way now. Armin, however, reminded his teammate that Mikasa had no gas left in her tank: as Connie was voicing his disbelief, the young blonde explained that he would give his gas to Mikasa, handing over his blades, too.

He had none left for himself, though, except the girl's broken one. "I'd rather avoid being eaten alive, if I can help it." He reasoned, before his friend took the blade out of his hand and dropped it over the side of the building: Mikasa looked at him, her determination clearly showing in her eyes and even in her usual, calm demeanor "Armin, I'm not abandoning you here."

"Well said." Alex interjected and got closer to the group. "So, how will you bring Armin along, with your depleted gas?" The monster asked and Armin looked back, toward the titan that had killed two class fifteens... "I have an idea! But it takes a couple of people, so you will have to make that call. As crazy as it sounds..."

"ARMIN, YOU ARE EITHER VERY BRAVE OR VERY CRAZY!" Conny yelled as he followed the big titan that was heading for the cluster of titans crowding HQ. Mikasa was off killing other titans. "Maybe..." Armin thought out loud: so far the plan was working wonderfully, as they were leading the big titan to their destination... All three of them had been quite shocked when Alex agreed to the plan they had hatched and grew claws that were as sharp as they were long: with a grin he had commented "I like your idea, Armin. You guys follow the big guy, I will help you killing the titans coming our way." All three of them had almost hurt their neck when they turned to watch the bioweapon jump around in a frenzy, jumping on the back of a 10 meter titan and slashing its nape before jumping on one only slightly smaller to completely cut its head and neck to ribbons, killing two in the span of six seconds.

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Thank you guys for reading this: if you liked the story so far leave a review to let me know where I could improve my sentences and grammar if you find anything.

I appreciate it!


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